The present invention relates to an image processing apparatus and method having a function of adjusting the image forming condition of image forming means.
Conventionally, as a method of adjusting the image processing characteristics of an image forming apparatus such as a copying machine, a printer, or the like, the following technique is known.
More specifically, in this technique, an image forming apparatus is turned on and a specific gradation test pattern is formed on a recording medium. Thereafter, the density of the gradation test pattern formed on the recording medium is read by image reading means, and correction data based on the read image information is fed back to means for determining an image forming condition such as .gamma. correction means. With this technique, image quality can be stabilized in correspondence with a variation in characteristics due to aging or a variation in environmental condition.
However, in a copying machine, a printer, or the like, the density of an output sample, which has just finished a fixing process is unstable.
For example, immediately after a thermal fixing process, a change in output toner image due to a change in temperature is large, and the physical properties of the toner on the output sample also change. As a result, the surface state of the output sample changes as the temperature of the sample becomes close to room temperature.
Furthermore, as is known, silicone oil is coated on the roller surface so as to prevent a toner image from becoming attached to a fixing roller, i.e., to improve separation characteristics. The silicone oil remains on the surfaces of a support member and a toner layer, and is absorbed in the support member as time elapses. This results in reductions in glossiness, density, and the like, and changes the optical density upon reading a toner image.
In the case of an ink-jet system, since ink dots formed on a recording medium are gradually dried, the optical density of an image changes.
In this manner, although the optical density of a gradation test pattern changes, since correction data is fed back to means for determining an image forming condition such as .gamma. correction means on the basis of the read information, an optimal image cannot be obtained.
On the other hand, in the conventional adjusting method, in an image reader, the amount of light emitted from a lamp used for reading changes as time elapses, and the reading condition changes depending on the degree of contamination of an optical system such as a reflecting mirror, a lens, and the like for focusing light emitted from the lamp.
In this case, the image forming condition is controlled under the changed reading condition, and it becomes difficult to accurately adjust the image processing condition of the image forming apparatus.
Furthermore, in the conventional adjusting method, when a recording medium formed with a gradation pattern (density data) and placed on an original table is to be read, if the recording medium is skewed or shifted, wrong data may be read. When correction data is fed back to the image forming condition based on the wrong data, an optimal image cannot be obtained.